Low liquid level indicator

Claim 2

A low liquid level indicator including a container having a liquid positioned therein the level of which is to be indicated, a source of direct current electrical energy, a probe associated wiTh said container, an AC coupling means, a bimetallic pulseproducing means coupled to said source of direct current electrical energy and to said AC coupling means for cyclically coupling said source of electrical energy to said probe through said AC coupling means, said bimetallic pulse-producing means including a bimetal blade having a fixed end connected to said AC coupling means, an electrical heater means positioned in heat exchange relationship to said bimetal blade, one terminal of said heater means being connected to said source of direct current electrical energy and the other terminal being connected to the free end of said bimetallic blade, and a stationary contact connected to ground and adapted to contact the free end of said bimetal blade, a low liquid level indicating means coupled to said probe and to said source of electrical energy, said probe including means cooperating with the liquid in said container for developing a first voltage level when said liquid is above a satisfactory operating level in said container and developing a second voltage level when said liquid is below a satisfactory operating level in said container, said indicating means including means responsive to said second voltage level for giving a warning indication when said liquid is below said satisfactory operating level.

Claim 3

A low liquid level indicator comprising a source of direct current electrical energy, a solid-state switching network having output electrodes and a control electrode, a warning means coupled to said source of electrical energy and the output electrodes of said solid-state switching network, a voltage divider comprising a resistor, a container having a liquid positioned therein, and a probe electrically insulated from said container, means connecting the junction of said resistor and said probe with said control electrode of said solid-state switching network, AC coupling means, means for cyclically coupling said source of electrical energy to said resister at its end opposite said junction through said AC coupling means, said last-mentioned means including a bimetal blade having one end thereof connected to said AC coupling means, an electrical heater means positioned in heat exchange relationship to said bimetal blade, one end of said electrical heater means being connected to said source of direct current electrical energy and the other end thereof connected to the other end of said bimetal blade, a stationary contact connected to ground, said other end of said bimetallic blade being in electrical contact with said stationary contact when said electrical heater means is unenergized and remaining in contact therewith until such time as said electrical heater means supplies a given amount of heat to said bimetal blade whereupon said other end of said bimetal blade moves out of engagement with said stationary contact and current through electrical heater means is interrupted, said probe including means for connecting said probe and said container through said liquid when said liquid is at a satisfactory operating level, the resistance value of said resistor and the impedance value of said probe, liquid and container being selected to provide a voltage level on the control electrode of said solid-state switching device to cause conduction of said solid-state switching network and energization of said warning means when the liquid is below a satisfactory operating level and another voltage level to cause nonconduction of said solid-state switching network when the liquid is above a satisfactory operating level.

Claim 4

A low liquid level indicator comprising a source of direct current electrical energy, a solid-state switching network having output electrodes and a control electrode, a warning means coupled to said source of electrical energy and the output electrodes of said solid-state switching network, a voltage divider comprising a resistor, a container having a liquid positioned therein, and a probe electrically insulated from said container, means connecting the junction of said resistor and said probe with said control electrode of said solid-state switching network, AC coupling means, means for cyclically coupling said source of electrical energy to said resister at its end opposite said junction through said AC coupling means, said last-mentioned means including a bimetal blade having one end thereof connected to said AC coupling means, an electrical heater means positioned in heat exchange relationship to said bimetal blade, one end of said electrical heater means being connected to said source of direct current electrical energy and the other end thereof connected to the other end of said bimetal blade, a stationary contact connected to ground, said other end of said bimetallic blade being in electrical contact with said stationary contact when said electrical heater means is unenergized and remaining in contact therewith until such time as said electrical heater means supplies a given amount of heat to said bimetal blade whereupon said other end of said bimetal blade moves out of engagement with said stationary contact and current through electrical heater means is interrupted, said probe including means for connecting said probe and said container through said liquid when said liquid is at a satisfactory operating level, the resistance value of said resistor and the impedance value of said probe, liquid and container being selected to provide a voltage level on the control electrode of said solid-state switching device to cause conduction of said solid-state switching network and energization of said warning means when the liquid is below a satisfactory operating level and another voltage level to cause nonconduction of said solid-state switching network when the liquid is above a satisfactory operating level.

Claim 5

The combination of claim 2 and further comprising a rectifying means connected to said junction and to said control electrode of said solid-state switch means for rectifying the AC signal emanating from said junction toward said control electrode.